The Underscores

QB64 prefixes "extended" features with an underscore to keep them from interfering with QBASIC types/variables. QBASIC considers the underscore to be a line-continuation character and ignores everything after the underscore. So you could do this to make a mouse subroutine compatible with both QBASIC and QB64, assuming that QB64 has a subroutine GETMOUSE that gets the x, y, and button positions into X, Y, and Z. FreeBASIC also decided to use underscores for a similar purpose.


X=-1
REGS.AX=3
CALL _GETMOUSE(x, y, z) 'QB64 getmouse
INTERRUPT(&H33, REGS, REGS) 'mouse using call interrupt
IF X=-1 THEN 'we are in QBASIC
X = REGS.CX
Y = REGS.DX
Z = REGS.BX
END IF